DOCSLIB.ORG

Sr Isotopic Variations Along the Juan De Fuca Ridge

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Sr Isotopic Variations Along the Juan De Fuca Ridge University of South Florida Scholar Commons Marine Science Faculty Publications College of Marine Science 9-1984 Sr Isotopic Variations along the Juan de Fuca Ridge Jacqueline Eaby U.S. Geological Survey, [email protected] David A. Clague U.S. Geological Survey John R. Delaney University of Washington Follow this and additional works at: https://scholarcommons.usf.edu/msc_facpub Part of the Life Sciences Commons Scholar Commons Citation Eaby, Jacqueline; Clague, David A.; and Delaney, John R., "Sr Isotopic Variations along the Juan de Fuca Ridge" (1984). Marine Science Faculty Publications. 1321. https://scholarcommons.usf.edu/msc_facpub/1321 This Article is brought to you for free and open access by the College of Marine Science at Scholar Commons. It has been accepted for inclusion in Marine Science Faculty Publications by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 89, NO. B9, PAGES 7883-7890, SEPTEMBER 10, 1984 Sr IsotopicVariations Along the Juande Fuca Ridge JACQUELINEEABY AND DAVID A. CLAGUE U.S. GeologicalSurvey, Menlo Park, California JOHN R. DELANEY OceanographyDepartment, University of Washington,Seattle Srisotopic ratios of 39glass and microcrystalline basalt samples along the Juan de Fuca Ridge and 1 glasssample from BrownBear Seamount are at the lowerend of the rangefor normalmid-oceanic ridge basalt(MORB)' the average87Sr/S6Sr ratio is 0.70249+ 0.00014(2-a). Althoughsubtle variations exist alongstrike of the ridge,the Sr isotopedata do not showsystematic variation relative to the proposed CobbHotspot. The isotopicdata are inconsistentwith an enrichedmantle-plume origin for the Cobb- EickelbergSeamount chain, as has beenproposed for Iceland,the Azores,and the Galapagosspreading center.Sr isotopicratios of samplescollected north and southof the Cobb offsetare identical,although minor elementratios indicate that theseregions have chemicallydistinct mantle sources. These distinct mantlesources may not havebeen separated long enough to developisotopic differences. INTRODUCTION characterizedby high 2ø6pb/2ø'*Pb,low 87Sr/86Sr,and high The hotspo•tmodel proposed by Wilson[1965] and Morgan •'•3Nd/•'•'•Nd.Geochemical variations of lavasalong hotspot/ [!973] explainsthe origin of linear seamountchains as the ridge systemsare interpretedto be the result of mixing be- result of movementof lithosphericplates over mantle plumes. tween enriched and normal MORB end-members [Schillin•t, The Cobb-EickelbergSeamount chain, in the northeastPaci- 1975a; Schillin•tet al., 1982a]. fic, trends northwestward from the Juan de Fuca Ridge and is The objectiveof thisstudy is to presentnew Sr isotopicdata interpretedto have a hotspot origin. A seamountat approxi- for lavas dredgedfrom the Juan de Fuca Ridge and to use these data to evaluate the mantle source characteristics of the mately lat 46øN on the axis of the Juan de Fuca Ridge (axial seamount)is coincidentwith the intersectionof the Cobb- Cobb Hotspot. EickelbergSeamount chain and the ridge; it is thought to be GEOLOGIC SETTING the site of presenthotspot activity, herein referred to as the CobbHotspot [Vogt and Johnson, 1975]. The Juande Fuca Ridge,which extends 500 km from the Detailed studiesof other mid-oceanicridge/hotspot systems, BlancoFracture Zone to the SovancoFracture Zone (Figure suchas Iceland [Hart et al., 1973; $chillin•h1973, 1975a], the 1),is a spreadingcenter of moderate rate, 30 •ma-x between Azores [White et el., 1975, 1976; $chillin•h 1975b], and the the Pacificand Juan de Fucaplates. Mor•tan [1973] proposed Galapagosspreading center [$chillin•l et el., 1982a;Verma and theexistence of a •otspoton theJuan de FucaRidge to Schilling,1982] showed that basalt erupted along deep mid- explainthe northwest trending linear seamount chain includ- oceanicridge segments(normal MORB) differs from basalt ingBrown Bear, Cobb, and Eickelberg seamounts. K-Ar ages erupted along topographic highs associatedwith islands fromHorton Seamount, located near the northwest end of the astride the ridge (enriched MORB). Normal MORB is seamountchain, indicate that the Cobb Hotspot has been a characterizedby low concentrationsof incompatibleelements; zoneof high volcanicproductivity for at least20 Ma [Turner light rare earth elementdepleted patterns; high K/Ba, K/Rb, et el., 1980]. and Zr/Nb ratios; low 8•Sr/S6Sr ratios; and high There are four morphologicallydistinct segmentsof the •'•3Nd/X'•'•Ndratios [White et el., 1975;DePaolo and Wass. Juande Fuca Ridge(Figure 2)'(1) A 90-km-long,linear, sym- erburg,1976]. These chemical characteristics are consistentmetrical southern ridge segmentnorth of the BlancoFracture with those of basalt derived from mantle sourceregions deple- Zone;(2) a 140-km-longcomplexly disturbed central segment, ted by previousmelting events[Kay et el., 1970]. Enriched recentlyoffset approximately 20 km westof the magneticaxis MORB, which has chemical affinities to oceanic island tho- of symmetry,which includes the axial seamount;(3) another leiites, differs from normal MORB by having higher con- 90-km-long,linear, symmetricalnorthern ridge segmentex- centrationsof incompatible elements;rare earth element pat- tendingnorthward to the Cobboffset (the tip of a northward ternsmore enriched in thelight elements; lo•wer K/Ba, K/Rb, propagatingrift [Johnsonetal., 1983]); and (4) the ridge north and Zr/Nb ratios; higher 8*Sr/8aSr ratios; and lower ofthe Cobb offset, referred to asthe Endeavor Ridge [Delaney x'•3Nd/X'•'•Ndratios than normalMORB [Bryanet el., 1976; et al., 1982]. White and Bryan, 1977; O'Nions et el., 1977]. Schilling[1973, Basalt collectedsouth of the Cobb offset (regions 1-3) is 1975b] and Schillinget el. [1982a] proposethat enriched predominan,tlyaphyric olivine- to quartz-normativetholeiite MORB is generatedfrom a nondepletedmantle source.Zind- slightlyto distinctlyenriched in iron and titaniumcompared let et el. [1982] propose a third chemically independent with normalMORB. Regionalvariations of FeO* (total iron mantle component,possibly related to recycledoceanic crust, calculatedas FeO) are plotted as a functionof latitude in Figure3. Ferrobasalt {> 10% FeO*) is particularly abundant Thispaper is not subjectto U.S.copyright. Published in 1984by at the southernend of region 1, and 20-30 km southof the the AmericanGeophysical Union. Cobb offset. The maximum iron and titanium enrichment in Paper nurlaber4B0708. the lavasoccurs behind zones identified as propagatingrifts in 7883 7884 EABY ET AL.' SR ISOTOPIC RATIOS ALONG JUAN DE FUCA RIDGE chemistry,and glasschemistry of a muchlarger set of samples will be discussedelsewhere (J. R. Delaney et al., unpublished data, 1984).All samplesare glassybasalt from the actively spreadingaxis and werechosen for their fresh•:essand spatial distribution.Samples along the ridgeand from the peak of the • I -• WelkerGuyol axial seamountare approximately25 km apart. ß • ß , •t • ANALYTICAL TECHNIQUES .- . •. ,' ', - • Hand-picked,fresh glasschips were rinsedin acetoneand __ ' • • ' ' ' •m,Chain • 'O DIlwood . washed with distilled water in an ultrasonic cleaner for 5 min. Microcrystalline-basaltsamples were ground to < 200 meshin .... , -- .'• i • a tungstencarbide shatterbox.Samples of powder or glass I. '/ ....,, , •o•LL/• :5 • 'a weighingapproximately 100 mg were dissolvedin HF and HC10,•, and Sr was separatedfrom the unspikedaliquots i i '1 '1 usingstandard ion-exchange chromatography. Mass analysis was done at the U.S. Geological Surveyin Menlo Park on a / . ' ' "•,• •'Y • • I • • 40øN / I '' I 1 •1 •1 I •.,..:S'o,."?.•I I 49 ø N 150ø 1400 I •0 ø 1200W Fig. 1. Seamount and ridge distribution in the northeast Pacific Ocean. The youngest seamount of the Cobb-Eickelberg Seamount chain occurs at the intersection of the seamount chain and the Juan de Fuca Ridge. Figure modified from Barr [ 1974]. %0 ENDEAVOUR . both regions [Hey and Wilson, 1982; Delaney et al., 1981; SEGMENT - 48øN Johnsonet al., 1983]. The petrologic diversity of lavas in re- (region 4) gions 1-3 may be the result of variable degreesof fractional crystallization[Clague and Bunch,1976] in magma chambers spatiallyassociated with propagatingrifts [Sintonet al., 1983]. COBB OFFSE'T Vogt and Byefly [1976] postulated that the iron and titanium enrichmentcould result from fractional crystallizationin a 47øN NORTHERN subaxial conduit transporting magma longitudinally away SEGMENT from the hotspot. (region 3) Basalt from region 4 is chemicallydistinct from basalt south of the Cobb offset. The lavas are not unusuallyenriched in iron and titanium but are enrichedin K20 (up to 0.56 wt %), Na20 (up to 3.36 wt %), and SiO: (up to 52.5 wt %). The CENTRAL P:Os/K:O ratios rangefrom 0.5 to 0.8 comparedwith P:O5 SEGMENT 46øN /K20 ratios of > 1.0 for lavas south of the Cobb offset (region 2) (J.R. Delaney et al., unpublisheddata, 1984).The P:Os/K:O ratios are probably indicative of mantle source regions [Clagueet al., 1981-1,thus suggestingthat lava from region4 is 4R derived from mantle sources distinct from those of lava from regions 1-3. 46 45 øN SAMPLE SELECTION A comprehensivesampling and surveyingprogram of the 4 500-km-long ridge segmentbetween the Sovancoand Blanco I 'if3 i n•q t2(1 124 fracturezones was initiated by the Universityof Washington in 1980 to characterizethe chemical,petrologic, and tectonic interaction among a spreading center of moderate rate, a I 44øN 131 o ',1/ 128oW 127ø w seamount-generatinghotspot, and propagatingrifts. Ratios of 87Sr/86Srwere determined
Load more

Recommended publications
  • Geology, Geochemistry and Earthquake History of Loieihi Seamount, Hawaiei's Youngest Volcano
    ARTICLE IN PRESS Chemie der Erde ] (]]]]) ]]]–]]] www.elsevier.de/chemer INVITED REVIEW Geology, geochemistry and earthquake history of Lo¯"ihi Seamount, Hawai"i’s youngest volcano Michael O. Garciaa,Ã, Jackie Caplan-Auerbachb, Eric H. De Carloc, M.D. Kurzd, N. Beckera aDepartment of Geology and Geophysics, University of Hawai"i, Honolulu, HI 96822, USA bAlaska Volcano Observatory, U.S.G.S., Alaska Science Center, Anchorage, AK 99508, USA cDepartment of Oceanography, University of Hawai"i, Honolulu, HI 96822, USA dDepartment of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA Received 6 June 2005; accepted 20 September 2005 Abstract A half-century of investigations are summarized here on the youngest Hawaiian volcano, Lo¯"ihi Seamount. It was discovered in 1952 following an earthquake swarm. Surveying in 1954 determined it has an elongate shape, which is the meaning of its Hawaiian name. Lo¯"ihi was mostly forgotten until two earthquake swarms in the 1970s led to a dredging expedition in 1978, which recovered young lavas. The recovery of young lavas motivated numerous expeditions to investigate the geology, geophysics, and geochemistry of this active volcano. Geophysical monitoring, including a real- time submarine observatory that continuously monitored Lo¯"ihi’s seismic activity for 3 months, captured some of the volcano’s earthquake swarms. The 1996 swarm, the largest recorded in Hawai"i, was preceded earlier in the year by at least one eruption and accompanied by the formation of a 300-m deep pit crater, Pele’s Pit. Seismic and petrologic data indicate that magma was stored in a 8–9 km deep reservoir prior to the 1996 eruption.
    [Show full text]
  • Posteruption Enhancement of Hydrothermal Activity: a 33-Year, Multieruption Time Series at Axial Seamount (Juan De Fuca Ridge)
    RESEARCH ARTICLE Posteruption Enhancement of Hydrothermal Activity: A 10.1029/2018GC007802 33‐Year, Multieruption Time Series at Axial Key Points: • Water column surveys, 1985‐2017, Seamount (Juan de Fuca Ridge) show that hydrothermal plume rise Edward T. Baker1,2 , Sharon L. Walker2 , William W. Chadwick Jr3 , height and turbidity identify the last 1,2 1,2 1,2 three Axial Seamount eruptions David A. Butterfield , Nathaniel J. Buck , and Joseph A. Resing • Posteruptive enhancement of 1 2 hydrothermal activity lasted 2‐5 Joint Institution for the Study of the Atmosphere and Ocean, University of Washington, Seattle, WA, USA, NOAA/ years posteruption, totaling Pacific Marine Environmental Laboratory, Seattle, WA, USA, 3NOAA Pacific Marine Environmental Laboratory, ~10 years over the survey duration Newport, OR, USA • Posteruption heat flux increased sixfold, implying that fluxes based on noneruptive activity alone will ‐ underestimate the long‐term flux Abstract Mid ocean ridge eruptions, initiating or revitalizing hydrothermal discharge and disrupting seafloor ecosystems, occur regularly as a consequence of plate spreading. Evaluating their impact on Supporting Information: long‐term hydrothermal discharge requires information on the scale and duration of any posteruption • Supporting Information S1 enhancement. Here we describe a unique hydrothermal plume time series of annual (or more frequent) • Figure S1 fi • Data Set S1 observations at Axial Seamount vent elds from 1985 through 2017, missing only 7 years. Axial, a hot spot • Data Set S2 volcano astride the Juan de Fuca Ridge, experienced eruptions in 1998, 2011, and 2015. In 1998 and 2011 • Data Set S3 lava flooded the SE caldera and south rift zone, but in 2015 most lava was extruded in a series of flows • Data Set S4 extending ~20 km down the north rift zone.
    [Show full text]
  • Cenozoic Changes in Pacific Absolute Plate Motion A
    CENOZOIC CHANGES IN PACIFIC ABSOLUTE PLATE MOTION A THESIS SUBMITTED TO THE GRADUATE DIVISION OF THE UNIVERSITY OF HAWAI`I IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN GEOLOGY AND GEOPHYSICS DECEMBER 2003 By Nile Akel Kevis Sterling Thesis Committee: Paul Wessel, Chairperson Loren Kroenke Fred Duennebier We certify that we have read this thesis and that, in our opinion, it is satisfactory in scope and quality as a thesis for the degree of Master of Science in Geology and Geophysics. THESIS COMMITTEE Chairperson ii Abstract Using the polygonal finite rotation method (PFRM) in conjunction with the hotspot- ting technique, a model of Pacific absolute plate motion (APM) from 65 Ma to the present has been created. This model is based primarily on the Hawaiian-Emperor and Louisville hotspot trails but also incorporates the Cobb, Bowie, Kodiak, Foundation, Caroline, Mar- quesas and Pitcairn hotspot trails. Using this model, distinct changes in Pacific APM have been identified at 48, 27, 23, 18, 12 and 6 Ma. These changes are reflected as kinks in the linear trends of Pacific hotspot trails. The sense of motion and timing of a number of circum-Pacific tectonic events appear to be correlated with these changes in Pacific APM. With the model and discussion presented here it is suggested that Pacific hotpots are fixed with respect to one another and with respect to the mantle. If they are moving as some paleomagnetic results suggest, they must be moving coherently in response to large-scale mantle flow. iii List of Tables 4.1 Initial hotspot locations .
    [Show full text]
  • Integrated 2D Geophysical Modeling Over the Juan De Fuca Plate Asif
    Integrated 2D geophysical modeling over the Juan de Fuca plate Asif Ashraf*, Irina Filina University of Nebraska-Lincoln Out of three oceanic plates subducting beneath North America along the Cascadia Subduction Zone, the Juan de Fuca (JdF) plate is the most intriguing one as it has an unusual seismicity pattern. The two other plates – the Explorer to the north and the Gorda to the south – are associated with a large number of earthquakes along the subduction zone. In contrast, JdF is seismically quiescent, so the inevitable and potentially devastating megathrust earthquake is expected in that region. To understand the tectonic complexity of the JdF subduction, it is important to understand the overall crustal architecture of the margin as well as to know physical properties (densities and magnetic susceptibilities) of the rocks of both oceanic and continental domains. Hence, we performed 2D integrated geophysical modeling along a published seismic reflection profile spanning from the Juan de Fuca spreading ridge to the High Cascades onshore. In our analysis, we have integrated multiple geophysical data from public sources, namely gravity and magnetic fields with seismic reflections and refractions. Our constructed 2D geophysical model starts from the Axial segment of the JdF spreading ridge. On the western side of the profile, gravity model requires lower densities of the mantle rocks associated with the Cobb hotspot. There are also two bathymetric seamounts near the oceanic ridge that have both gravity and magnetic signatures. Our profile crosses the pseudofault zones that require lower crustal densities with respect to adjacent oceanic crusts. We interpret this as evidence of extensive faulting in that region making the pseudofaults zones of weakness within the JdF plate.
    [Show full text]
  • Seismic Precursors and Magma Ascent Before the April 2011 Eruption at Axial Seamount
    LETTERS PUBLISHED ONLINE: 10 JUNE 2012 | DOI: 10.1038/NGEO1490 Seismic precursors and magma ascent before the April 2011 eruption at Axial Seamount R. P. Dziak1*, J. H. Haxel1, D. R. Bohnenstiehl2, W. W. Chadwick Jr1, S. L. Nooner3, M. J. Fowler1, H. Matsumoto1 and D. A. Butterfield4 Volcanoes at spreading centres on land often exhibit seismicity seismicity associated with the opening of a hydraulic fracture. As and ground inflation months to years before an eruption, magma leaves the reservoir, the overlying ground surface typically caused by a gradual influx of magma to the source reservoir1–4. subsides. The timing of this deflation signal often coincides with Deflation and seismicity can occur on time scales of hours to seismic activity, but there also are examples where the earth- days, and result from the injection of magma into adjacent quake swarms are delayed by several hours relative to the onset rift zones5–8. Volcanoes at submarine rift zones, such as of deflation2,5,6. Similarly, surface eruptions have been reported Axial Seamount in the northeast Pacific Ocean, have exhibited contemporaneously or up to several hours after deflation began. In similar behaviour9–12, but a direct link between seismicity, other cases, dykes do not break the surface and eruptions are absent seafloor deformation and magma intrusion has never been altogether. In comparison, only two other submarine-rift-zone demonstrated. Here we present recordings from ocean-bottom eruptions have been observed in situ, one with seismic and temper- hydrophones and an established array of bottom-pressure ature sensors (2005–2006 East Pacific Rise eruption sequence) and recorders that reveal patterns of both microearthquakes and the other with geodetic sensors (1998 Axial Seamount; refs 10–12).
    [Show full text]
  • Microbiology of Seamounts Is Still in Its Infancy
    or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of The approval portionthe ofwith any articlepermitted only photocopy by is of machine, reposting, this means or collective or other redistirbution This article has This been published in MOUNTAINS IN THE SEA Oceanography MICROBIOLOGY journal of The 23, Number 1, a quarterly , Volume OF SEAMOUNTS Common Patterns Observed in Community Structure O ceanography ceanography S BY DAVID EmERSON AND CRAIG L. MOYER ociety. © 2010 by The 2010 by O ceanography ceanography O ceanography ceanography ABSTRACT. Much interest has been generated by the discoveries of biodiversity InTRODUCTION S ociety. ociety. associated with seamounts. The volcanically active portion of these undersea Microbial life is remarkable for its resil- A mountains hosts a remarkably diverse range of unusual microbial habitats, from ience to extremes of temperature, pH, article for use and research. this copy in teaching to granted ll rights reserved. is Permission S ociety. ociety. black smokers rich in sulfur to cooler, diffuse, iron-rich hydrothermal vents. As and pressure, as well its ability to persist S such, seamounts potentially represent hotspots of microbial diversity, yet our and thrive using an amazing number or Th e [email protected] to: correspondence all end understanding of the microbiology of seamounts is still in its infancy. Here, we of organic or inorganic food sources. discuss recent work on the detection of seamount microbial communities and the Nowhere are these traits more evident observation that specific community groups may be indicative of specific geochemical than in the deep ocean.
    [Show full text]
  • High-Resolution Surveys Along the Hot Spot–Affected Galapagos Spreading Center: 1
    University of South Carolina Scholar Commons Faculty Publications Earth, Ocean and Environment, School of the 9-27-2008 High-Resolution Surveys Along the Hot Spot–Affected Galapagos Spreading Center: 1. Distribution of Hydrothermal Activity Edward T. Baker Rachel M. Haymon University of California - Santa Barbara Joseph A. Resing Scott M. White University of South Carolina - Columbia, [email protected] Sharon L. Walker See next page for additional authors Follow this and additional works at: https://scholarcommons.sc.edu/geol_facpub Part of the Earth Sciences Commons Publication Info Published in Geochemistry, Geophysics, Geosystems, Volume 9, Issue 9, 2008, pages 1-16. Baker, E. T., Haymon, R. M., Resing, J. A., White, S. M., Walker, S. L., Macdonald, K. C., Nakamura, K. (2008). High-resolution surveys along the hot spot–affected Galapagos Spreading Center: 1. Distribution of hydrothermal activity. Geochemistry, Geophysics, Geosystems, 9 (9), 1-16. © Geochemistry, Geophysics, Geosystems 2008, American Geophysical Union This Article is brought to you by the Earth, Ocean and Environment, School of the at Scholar Commons. It has been accepted for inclusion in Faculty Publications by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. Author(s) Edward T. Baker, Rachel M. Haymon, Joseph A. Resing, Scott M. White, Sharon L. Walker, Ken C. Macdonald, and Ko-ichi Nakamura This article is available at Scholar Commons: https://scholarcommons.sc.edu/geol_facpub/67 Article Geochemistry 3 Volume 9, Number 9 Geophysics 27 September 2008 Q09003, doi:10.1029/2008GC002028 GeosystemsG G ISSN: 1525-2027 AN ELECTRONIC JOURNAL OF THE EARTH SCIENCES Published by AGU and the Geochemical Society High-resolution surveys along the hot spot–affected Gala´pagos Spreading Center: 1.
    [Show full text]
  • Anatomy of an Active Submarine Volcano
    Downloaded from geology.gsapubs.org on July 28, 2014 Anatomy of an active submarine volcano A.F. Arnulf1, A.J. Harding1, G.M. Kent2, S.M. Carbotte3, J.P. Canales4, and M.R. Nedimović3,5 1Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California–San Diego, La Jolla, California 92093, USA 2Nevada Seismological Laboratory, 0174, University of Nevada–Reno, Reno, Nevada 89557, USA 3Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA 4Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02540, USA 5Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H4J1, Canada ABSTRACT To date, seismic experiments have been one Most of the magma erupted at mid-ocean ridges is stored in a mid-crustal melt lens that lies of the keys in our understanding of the inter- at the boundary between sheeted dikes and gabbros. Nevertheless, images of the magma path- nal structure of volcanic systems (Okubo et al., ways linking this melt lens to the overlying eruption site have remained elusive. Here, we have 1997; Kent et al., 2000; Zandomeneghi et al., used seismic methods to image the thickest magma reservoir observed beneath any spreading 2009; Paulatto et al., 2012). However, most ex- center to date, which is principally attributed to the juxtaposition of the Juan de Fuca Ridge periments, especially subaerial-based ones, are with the Cobb hotspot (northwestern USA). Our results reveal a complex melt body, which restricted to refraction geometries with limited is ~14 km long, 3 km wide, and up to 1 km thick, beneath the summit caldera.
    [Show full text]
  • Aula 4 – Tipos Crustais Tipos Crustais Continentais E Oceânicos
    14/09/2020 Aula 4 – Tipos Crustais Introdução Crosta e Litosfera, Astenosfera Crosta Oceânica e Tipos crustais oceânicos Crosta Continental e Tipos crustais continentais Tipos crustais Continentais e Oceânicos A interação divergente é o berço fundamental da litosfera oceânica: não forma cadeias de montanhas, mas forma a cadeia desenhada pela crista meso- oceânica por mais de 60.000km lineares do interior dos oceanos. A interação convergente leva inicialmente à formação dos arcos vulcânicos e magmáticos (que é praticamente o berço da litosfera continental) e posteriormente à colisão (que é praticamente o fechamento do Ciclo de Wilson, o desparecimento da litosfera oceânica). 1 14/09/2020 Curva hipsométrica da terra A área de superfície total da terra (A) é de 510 × 106 km2. Mostra a elevação em função da área cumulativa: 29% da superfície terrestre encontra-se acima do nível do mar; os mais profundos oceanos e montanhas mais altas uma pequena fração da A. A > parte das regiões de plataforma continental coincide com margens passivas, constituídas por crosta continental estirada. Brito Neves, 1995. Tipos crustais circunstâncias geométrico-estruturais da face da Terra (continentais ou oceânicos); Característica: transitoriedade passar do Tempo Geológico e como forma de dissipar o calor do interior da Terra. Todo tipo crustal adveio de um outro ou de dois outros, e será transformado em outro ou outros com o tempo, toda esta dança expressando a perda de calor do interior para o exterior da Terra. Nenhum tipo crustal é eterno; mais "duráveis" (e.g. velhos Crátons de de "ultra-longa duração"); tipos de curta duração, muitas modificações e rápida evolução potencial (como as bacias de antearco).
    [Show full text]
  • Effect of Subduction Zones on the Structure of the Small-Scale Currents at Core-Mantle Boundary
    Effect of Subduction Zones on the Structure of the Small-Scale Currents at Core-Mantle Boundary. Sergey Ivanov1, Irina Demina1, Sergey Merkuryev1,2 1St-Petersburg Filial of Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio wave Propagation (SPbF IZMIRAN) 2Saint Petersburg State University, Institute of Earth Sciences Universitetskaya nab., 7-9, St. Petersburg, 199034, Russia [email protected] Abstract. The purpose of this work is to compare kinematics of small-scale current vortices located near the core-mantle boundary with high-speed anomalies of seismic wave velocity in the lowest mantle asso- ciated with the subduction zones. The small-scale vortex paths were early obtained by the authors in the frame of the macro model of the main geomagnetic field sources. Two sources were chosen whose kine- matics are characterized by the complete absence of the western drift and whose paths have a very com- plex shape. Both sources are located in the vicinity of the subduction zones characterized by the extensive coherent regions with increased speed of seismic waves in the lowest mantle. One of them is geograph- ically located near the western coast of Canada and the second one is located in the vicinity of Sumatra. For this study we used the global models of the heterogeneities of seismic wave velocity. It was obtained that the complex trajectories of the vortices is fully consistent with the high-speed anomalies of seismic wave velocity in the lowest mantle. It can be assumed that mixing up with the matter of the lowest man- tle, the substance of the liquid core rises along the lowest mantle channel and promotes its further in- crease.
    [Show full text]
  • Axial Seamount
    AXIAL SEAMOUNT - WIRED AND RESTLESS: A Cabled Submarine Network Enables Real-time, Tracking of a Mid-Ocean Ridge Eruption and Live Video of an Active Hydrothermal System Juan de Fuca Ridge, NE Pacific John R. Delaney1, Deborah S. Kelley1, Aaron Marburg2, Kim Juniper3 and Friedrich Knuth4 Mark Stoermer1, and Hunter Hadaway1, University of Victoria3 Ocean Networks Canada,Victoria School of Oceanography1 and Applied Physics B.C., Canada; 4 Rutgers University, Department of Marine Laboratory2 University of Washington and Coastal Sciences, New Brunswick, Seattle, WA, 98195 New Jersey Abstract—The most scientifically diverse and technologically understood owing to their remote locations beneath one to four advanced component of the National Science Foundations’ kilometers of seawater. As a consequence, submarine volcano- $386M investment in the Ocean Observatories Initiative (OOI), hydrothermal systems have never been observed-monitored involves 900 kilometers of high power and bandwidth electro- continuously. Nor have their immediate effects on overlying optical cable extending from Pacific City, OR, across active marine ecosystems been assessed because they are most active portions of the Juan de Fuca tectonic plate and up into the just before, during, and shortly after unpredictable eruptions overlying ocean. Completed on time and under budget in when the systems are the most energetic. Tracking the long- October, 2014, this mesoscale fiber-optic sensor array enables term behavior of even a small section of this powerful real-time, high-bandwidth, 2-way communication with seafloor planetary-scale submarine MOR could contribute substantially and water-column sensor networks across: 1) a portion of the to our understanding of a host of complex oceanic processes global Mid-Ocean Ridge (MOR), 2) a section of the Cascadia Subduction Zone, and, 3) a cross-section of the California triggered by numerous eruptions along this global submarine Current, a component of the North Pacific Gyre.
    [Show full text]
  • A 65 K.Y. Time Series from Sediment-Hosted Glasses Reveals Rapid Transitions in Ocean Ridge Magmas
    A 65 k.y. time series from sediment-hosted glasses reveals rapid transitions in ocean ridge magmas David J. Ferguson1,2*, Yinqi Li1,3, Charles H. Langmuir1, Kassandra M. Costa4,5, Jerry F. McManus4,5, Peter Huybers1, and Suzanne M. Carbotte4 1Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA 2School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK 3School of Earth Sciences, Zhejiang University, Hangzhou 310027, China 4Lamont-Doherty Earth Observatory (LDEO), Columbia University, Palisades, New York 10964, USA 5Department of Earth and Environmental Sciences, Columbia University, New York, New York 10027, USA ABSTRACT 2013; Portner et al., 2015). The extent to which Studies of ocean ridge magmatism have been hampered by the difficulty in construct- such glasses might be preserved in older sedi- ing time-series data over more than a few thousand years. Sediment rapidly covers newly ments and over longer time periods, however, formed ocean crust, and older rocks, even when recovered from fault scarps, cannot be dated has not previously been demonstrated. Here we accurately. Ridge eruptions, however, disperse pyroclastic glass over distances as far as 5 show using a piston core that reached 600 ka km, and these glasses have been shown to persist for thousands of years in on-ridge sediment basement that ancient glasses are indeed pre- push cores. Here we present data on such glasses from a piston core that impacted basement served and permit high-resolution observations in much older (600 ka) sediment. The age of deposition was determined using established over tens of thousands of years.
    [Show full text]